/**
 * Created by brss on 2018/8/29.
 */
public class LoopQueue<E> implements Queue<E> {

    private E[] data;
    private int front, tail;//队首索引/下一个入队索引
    private int size;//有效元素

    public LoopQueue(int capacity) {
        //循环队列会有意识的浪费一个空间
        data = (E[])new Object[capacity+1];
        front = 0;
        tail = 0;
        size = 0;
    }
    public LoopQueue(){
        this(10);
    }

    /**
     * 循环队列会有意识的浪费一个空间,真正能存放数据的数量要-1
     * @return
     */
    public int getCapacity(){
        return data.length - 1;
    }

    @Override
    public boolean isEmpty(){
        return front==tail;
    }

    @Override
    public int getSize(){
        return size;
    }

    @Override
    public void enqueue(E e) {

        //数组是否满
        if ( (tail + 1) % data.length == front )
            resize( getCapacity()*2 );

        data[tail] = e;
        tail = (tail+1)%data.length;
        size++;
    }
    @Override
    public E dequeue(){
        if (isEmpty()) {
            throw new IllegalArgumentException("Cannot dequeue from an empty queue.");
        }
        E ret = data[front];
        data[front] = null;
        front = (front+1) % data.length;
        size--;
        if (size == getCapacity() / 4 && getCapacity()/2 != 0)
            resize(getCapacity()/2);
        return ret;
    }

    @Override
    public E getFront(){
        if (isEmpty()) {
            throw new IllegalArgumentException("Queue is empty.");
        }
        return data[front];
    }

    private void resize(int newCapacity) {
        E[] newData = (E[])new Object[newCapacity + 1];
        for (int i = 0 ; i < size ; i++) {
            newData[i] = data[(front+i)%data.length];
        }
        data = newData;
        front = 0 ;
        tail = size;
    }

    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();
        res.append(String.format("Queue:size = %d , capacity = %d \n",size,getCapacity()));
        res.append("front [");
        for (int i = front ; i !=tail ; i = (i+1)%data.length ){
            res.append(data[i]);
            if ( (i+1)%data.length != tail )
                res.append(", ");
        }
        res.append("] tail");
        return res.toString();
    }
    public static void main(String[] args) {
        LoopQueue<Integer> queue = new LoopQueue<>();
        for (int i = 0 ; i < 10 ; i++) {
            queue.enqueue(i);
            System.out.println(queue);
            if (i % 3 == 2) {
                queue.dequeue();
                System.out.println(queue);
            }
        }

    }
}
